Radiolytic behavior and effect in nuclear reactor coolants: A focus on ammonia and hydrazine

Abstract

Coolant selection is intricately linked to the design and type of the nuclear reactor. To mitigate the corrosion of structural materials, the water chemistry of the primary circuit must be carefully managed. Usually, substances such as hydrogen, ammonia, and hydrazine are employed in the reactor's primary coolant. Among these additives, ammonia and hydrazine, which are nitrogen-containing additives, undergo a series of radiolysis reactions in the reactor, and the oxidation environment of the system is altered. In this review, published studies on the radiolytic behavior of ammonia and hydrazine were summarized and analyzed. For ammonia coolants, the ·OH radicals produced by water radiolysis react rapidly with NH₃. The radiolysis product of ammonia, ·NH₂ reacted with oxidizing species such as H₂O₂, ·OH, and O₂. Under aerobic conditions, the radiolysis of ammonia solutions primarily led to the production of NO_x⁻. For hydrazine coolants, NH₃, H₂, and N₂ were formed by thermal decomposition and radiolysis. N₂H₄ directly inhibited the formation of H₂O₂ and nitrogen oxides due to its strong reducibility and ability to remove O₂, ·OH, and H₂O₂. As the irradiation continued, NH₃ was consumed and its concentration decreased, the pH of coolant tended to decrease with further increases in absorbed dose.